<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        var score = prompt('输入成绩');
        if (score >= 90){
            alert('A')
        }else if (score>=80 ){
            alert('B')
        }else if (score>=70){
            alert('C')
        }else if (score>=60){
            alert('D')
        }else{
            alert('E')
        }
    </script>
</head>
<body>

</body>
</html>